1. Field of the Invention
The present invention relates to an ignition apparatus for an internal combustion engine having an igniter.
2. Description of Related Art
Conventionally, an ignition apparatus having an igniter has been disclosed to control ignition timing of an internal combustion engine (hereinafter, referred as an engine) by controlling primary current of the ignition coil assembly (see Japanese Unexamined Patent Publication No. H6-317243).
As shown in a circuit diagram in FIG. 6, in the ignition apparatus, a switching device 100, which regulates switching a coil current supplied to an ignition coil assembly 400, is connected with a Zener diode 200, which is a protection element for protecting an igniter 300 from an external surge. The igniter 300 includes the switching device 100 and the Zener diode 200.
Specifically, a cathode of the Zener diode 200 is connected to an input terminal 10, to which an ignition signal is inputted, and an anode of the Zener diode 200 is connected to a ground (GND) terminal 20, which is connected to a ground. Here, the ignition signal is inputted to the switching device 100 through the input terminal 10. A battery terminal 30 is connected to a battery. In the above connection state, a voltage-clamp function of the Zener diode 200 protects the switching device 100 from being applied with a high voltage even when the external surge is generated.
Recently, in some cases, the ignition apparatus having the igniter is mounted above a corresponding one of cylinders of the engine. Therefore, a length of a signal wire electrically connecting between the ignition apparatus and an engine control unit (ECU) may be increased, and as a result, a wire capacity of the signal wire may become larger.
In this state, a positive potential is selectively stored in the wire capacity by rectification of the Zener diode 200 in a circuit with the Zener diode 200 as shown in FIG. 6 when a radio current is generated around the signal wire by a strong electric field due to a broadcast station and a radio equipment. Then, a potential level, which is supposed to indicate a low level of an ignition input signal inputted to the ignition apparatus through the input terminal 10, is falsely increased to exceed a proper value for the low level of the ignition signal. Then, the igniter 300 falsely turns on the switching device 100 based on a false signal with the false potential level, and this may result in falsely operating the ignition apparatus.